1. Field of the Invention
The present invention relates to a sensor device for determining at least one parameter of a fluid medium flowing through a duct.
2. Description of the Related Art
From the existing art, numerous methods and devices are known for determining at least one flow property of fluid media, i.e. of liquids and/or gases. Among the flow properties, possible parameters can include any measurable physical and/or chemical properties that quantify or qualify a flow of the fluid medium. In particular, this can be a flow speed and/or a mass flow and/or a volume flow.
In the following, the present invention is described in particular with reference to so-called hot-film air mass sensors, as known for example from Konrad Reif (pub.): Sensoren im Kraftfahrzeug [Sensors in the Motor Vehicle], 1st ed. 2010, pp. 146-148. Such hot-film air mass sensors are as a rule based on a sensor chip, in particular a silicon sensor chip, for example having a sensor membrane as a measurement surface or sensor area over which the flowing fluid medium can flow. As a rule, the sensor chip includes at least one heating element as well as at least two temperature sensors that are for example situated on the measurement surface of the sensor chip, the one temperature sensor being positioned upstream from the heating element and the other temperature sensor being positioned downstream from the heating element. From an asymmetry of the temperature profile acquired by the temperature sensors, influenced by the flow of the fluid medium, a mass flow and/or volume flow of the fluid medium can be inferred.
Hot-film air mass sensors are standardly realized as sensor plugs that can be placed in a flow tube fixedly or exchangeably. For example, this flow tube can be an intake manifold of an internal combustion engine. Here, a partial flow of the medium flows through at least one main duct provided in the hot-film air mass sensor. Between the inlet and the outlet of the main duct, there is fashioned a bypass duct. In particular, the bypass duct is fashioned such that it has a curved segment for deflecting the partial flow of the medium entering through the inlet of the main duct, the curved segment transitioning, in its further course, into a segment in which the sensor chip is situated. The last-named segment is the actual measurement duct in which the sensor chip is situated.
Published international patent application document WO 02/084226 A1 discloses a sensor chip having potential surfaces for avoiding contamination on the sensor chip.
Published German patent application document DE 10 2010 020 264 A1 discloses a hot-film air mass sensor having a housing made of plastic that has an electrically insulating effect. In the housing, a flow duct is fashioned and there is situated a sensor element that acquires the air mass flowing in the flow duct. A part of the flow duct has electrostatically dissipative properties.
Published international patent application document WO 02/073140 A2 discloses a sensor chip having an additional heating unit for preventing contamination on the sensor chip.
Despite the numerous advantages of the methods known from the existing art for avoiding adhesion of particles carrying an electrical charge that impinge on the sensor area, there is still potential for improvement in these methods. For example, impinging particles carrying an electrical charge have up to now inadequately been kept away from the sensor area.